JPH0561815U - Optical head of optical disk device - Google Patents

Abstract

(57) [Abstract] [Purpose] To stabilize the frequency characteristics of the optical head of an optical disc to exceed 1 kHz. [Structure] Two laminated piezoelectric elements 1 each including a lens unit 3
Fixed to the movable body 2 by means of 2, and the two laminated piezoelectric elements 1
In the arrangement relationship of No. 2, the positions are equal distances a that pass through the center of gravity P of the lens unit 3 and face each other about the center of gravity 16 that is horizontal to the optical disc surface 17, and
The focused beam 9 of the laser beam for reading the signal of the optical disc A is arranged so as to pass between the two laminated piezoelectric elements 12.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical head mounted in an optical disk access mechanism in an optical disk device, and more particularly to a drive mechanism having a small displacement access function that enables the optical head itself to move at high speed.

[0002]

[Prior Art]

 FIG. 6 is a schematic perspective view of a conventional optical head and a movable device. FIG. 7 is a vertical sectional view passing through the center of an objective lens of a conventional optical head unit. As shown in FIG. 6, a conventional optical head access mechanism using a linear motor system is constructed by integrating a lens unit 3 and a movable body 2. The linear motor includes a side yoke 5 having a permanent magnet 6 fixed to the inner surface of a U-shaped member, a magnetic yoke 1 including a center yoke 4, and a coil 7 of the movable body 2. The coil 7 is wound around both sides of the lens unit 3 of the movable body 2 whose movement is held by the slide bearing 8, and the center yoke 4 is inserted therein. In order to access the optical head, a current is passed through the coil 7 placed in the magnetic field of the magnetic yoke 1 to move the movable body 2 in the radial direction of the optical disc A in the direction of arrow X in the figure. By controlling the current passed through the coil 7, it is possible to access the target track of the optical disc A.

Next, in FIG. 7, reference numeral 9 is a focused beam of a laser beam from a light source unit having a relay lens for automatic focal length adjustment, which is installed at another position. The focused light 9 is applied to the optical head in parallel to the optical disc surface 17, and the focused light passage hole 20 formed in the movable body 2 and the focused light passage formed in the lens unit 3 are transmitted. The light passes through the hole 21 and is reflected upward by the prism lens 10 of the lens unit 3 at right angles. The focused light 9 reflected at a right angle is converged by the objective lens 11 and applied to the optical disc A.

[0004]

[Problems to be solved by the device]

 By the way, according to the structure of the optical head of the conventional optical disk apparatus as described above, the large stroke movement and the minute stroke movement of the optical head are handled only by the linear motor. However, the conventional optical head has a structure in which the movable body and the lens unit are integrated, and there is a tendency that the weight of the movable optical head is inevitably large. For example, in order to realize high-density recording on an optical disc, the track interval of the optical disc must be smaller than the conventional track interval. Trackability is needed. However, with the conventional optical head, there is a limit to the high-speed access operation to each track of this high density recording type optical disk, and it is extremely difficult to keep the frequency characteristic of the optical head stable at 1 KHz or more. It was a problem.

[0005]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention has a lens unit having an objective lens and a prism lens in a cylindrical body, and a movable body for moving the lens unit in the radial direction of the optical disc. In the optical head of the optical disc device described above, the lens unit is fixed to the movable body through two laminated piezoelectric elements, and the lens unit is vertically moved about a horizontal center of gravity line passing through the center of gravity of the lens unit. The two laminated piezoelectric elements are arranged at equidistant relative positions and in such a position that the focused light of the laser beam for reading the signal of the optical disc passes between the two laminated piezoelectric elements. The present invention provides an optical head of an optical disk device, which is characterized by being arranged.

[0006]

[Action]

 As described above, the optical head itself is provided with an access function by mounting the lens unit on a movable body using the laminated piezoelectric element and using the laminated piezoelectric element as a driving element of the optical head section. You can The access function of the laminated piezoelectric element can be driven at a higher speed than the access function of the conventional linear motor. In order to stably maintain the frequency characteristics of the optical head at 1 KHz or more by the composite type access function, drive the linear motor of the same structure as before in the frequency band of several hundred Hz or less, It is sufficient to drive the optical head unit according to the invention.

[0007]

【Example】

 Hereinafter, the optical head of the optical disk device of the present invention will be described in detail with reference to the accompanying drawings. In the embodiments described below, the same reference numerals will be used for the same or corresponding components as in FIGS. FIG. 1 is a schematic perspective view showing an embodiment of the optical head of the present invention. FIG. 2 is a vertical sectional view through the center of the objective lens of the optical head unit of the present invention.

In FIG. 1, the focused light 9 of the laser beam for reading the signal of the optical disc is focused servo by a relay lens inside the light source unit fixed at another position, so that the optical head portion is in the radial direction of the optical disc. It is only necessary to move in the direction of the arrow X in the figure.

As described above, the movement of the optical head of the present invention is performed by the linear motor unit having the same structure as the conventional one in the frequency band of several hundred Hz or less. Further, the optical head unit is driven in the frequency band higher than that. In the present invention, in order to drive the optical head unit, a lens unit 3 which is conventionally integrated with the movable body 2 is provided independently of the movable body 2, and the lens unit 3 is traversed. Two laminated piezoelectric elements 12 having a width sufficient to suppress the inertia moment in the plane direction are used to mount the movable body 2 on the movable body 2.

In this embodiment, a laminated piezoelectric element is used as a drive element of the optical head unit. The laminated piezoelectric element has a smaller displacement amount but a quicker response than the bimorph piezoelectric element. It is characterized by having high frequency characteristics. As described above, when performing high-density recording on an optical disk, the optical head needs to have high tracking ability. It is very effective to use the laminated piezoelectric element having a high frequency characteristic as a driving element in order to obtain an optical head having a high followability.

Next, the structure of the optical head unit of the present invention will be described with reference to FIG. The lens unit 3 is a cylinder in which a prism lens 10 and an objective lens 11 are mounted, and a hole 14 through which the focused light 9 passes is formed on one side surface. On the side surface of the lens unit 3 on which the focused light passage hole 14 is formed, the center of gravity line 16 parallel to the optical disk surface 17 passing through the center of gravity P of the lens unit 3 is perpendicular to the optical disk surface 17. One of the laminated piezoelectric elements 12 is mounted at a position equidistant to and facing each other. Further, the other of the laminated piezoelectric elements 12 is fixed to the movable body 2, respectively. At this time, the focused light passage hole 14 is formed between the two laminated piezoelectric elements 12. Further, a focused light passage hole 13 is also formed in the movable body 2 with the same center as the focused light passage hole 14. Due to these arrangements, the focused light 9 passes between the two laminated piezoelectric elements 12 described above, and the laminated piezoelectric element 12 does not obstruct the path of the focused light 9.

By supporting the lens unit 3 with the two laminated piezoelectric elements 12 as described above, it is possible to minimize an unnecessary rotational moment. Even if a slight rotation moment is generated, the two laminated piezoelectric elements 12 are arranged at an equal distance a from the center of gravity line 16 in the longitudinal sectional direction in which the inertia moment of the lens unit 3 is large. Since it is arranged at the position, stable control is possible.

Next, the relationship between the mounting position of the laminated piezoelectric element 12, the position of the center of gravity of the lens unit 3 and the moment of inertia will be described. In order to extend the frequency characteristics of the optical head, it is necessary to prevent external force from acting in directions other than the stacking direction in which the stacked piezoelectric element 12 is movable. For that purpose, the weight of the lens unit 3, which is a direct load of the laminated piezoelectric element 12, is reduced as much as possible, and the two laminated piezoelectric elements 12 are separated from the center line 16 of the lens unit 3 and so on. It is important to design at the distance a to minimize the generation of unnecessary rotational moment.

For example, as shown in FIG. 3, when the lens unit 3 is supported by using one laminated piezoelectric element 12, the lens unit 3 is supported by the side surface on which the focused light passage hole 14 is formed. If the driving fulcrum is not on the center of gravity 16 of the lens unit 3, rotational moment will occur. However, in reality, as shown in FIG. 4, the drive fulcrum is displaced from the center of gravity line 16 in the horizontal direction due to the focused light passage hole 14. In such arrangement of the laminated piezoelectric element, the rotational energy generated by the moment of inertia in the longitudinal section due to the weight of the lens unit 3 and the moment of inertia in the lateral section due to the driving of the laminated piezoelectric element 12 is Since the lens unit 3 receives it in a complex manner, the lens unit 3 has complicated movements.

In addition to the one laminated piezoelectric element 12, another laminated piezoelectric element is mounted so as to face the center of gravity line 16, that is, the laminated piezoelectric element 12 is attached to the optical disk. When two pieces are supported side by side in the horizontal direction with respect to the surface 17, the rotational energy due to the moment of inertia in the cross-sectional direction is smaller than in the case of FIG. However, in reality, the moment of inertia of the vertical section is much larger than the moment of inertia of the horizontal section of the lens unit 3. Therefore, even if the two laminated piezoelectric elements are mounted in the horizontal direction on the optical disk surface 17 as described above, the frequency characteristic of the optical head cannot be extended by receiving the inertia moment in the vertical cross-sectional direction.

Next, in the case of the optical head shown in FIG. 5, the lens unit 3 is formed by using one laminated piezoelectric element 12, and the lens unit 3 is provided with the focused light passage hole. It supports from the opposite side. In the arrangement of the single laminated piezoelectric element 12 shown in FIG. 5, the laminated piezoelectric element 12 can be arranged without considering the position of the focused light passage hole. Here, as described above, it is important that the driving fulcrum of the laminated piezoelectric element 12 is on the center line 16 of the lens unit 3. However, in reality, it is impossible to dispose the laminated piezoelectric element 12 so as to eliminate the rotational moment accurately, and it is impossible to combine the rotational energy in the same manner as in the embodiment of FIG. I will receive it.

On the other hand, if the two laminated piezoelectric elements 12 can be mounted on the side surface of the lens unit 3 opposite to the incident direction of the focused light 9, the focused light 9 and the laminated piezoelectric element 12 can be mounted. It is only necessary to consider the center of gravity P of the lens unit 3 and the inertia moment without considering the mounting position of the optical head, and the design of the optical head is easy. However, usually, since there is a spindle motor and the like, when the optical head approaches the inner peripheral portion of the optical disc A, a problem such as space arises, and as shown in FIG. It is difficult to dispose the laminated piezoelectric element 12 on the opposite side surface of the lens unit 3.

As described above, in the case where the lens unit is supported by one laminated piezoelectric element or when two laminated piezoelectric elements are mounted in the lateral direction with respect to the optical disc surface 17, whichever piezoelectric element is mounted is used. Also in this case, the frequency characteristic of the optical head becomes a limit value of about 1 KHz even though the weight of the lens unit 3 is as light as 0.6 g.

In FIG. 2, the center of gravity P of the lens unit 3 is not on the optical axis of the focused light 9 due to the structure of the lens unit 3, but even if the center of gravity P is deviated from the optical axis. Since the two laminated piezoelectric elements 12 are arranged at positions equidistant from the center of gravity line 16, there is no problem even if the center of gravity P is not on the optical axis.

The laminated piezoelectric elements 12 of the present invention are arranged two in the vertical direction with respect to the optical disk surface 17 in consideration of the inertia moment in the longitudinal section. This is because, as described above, the moment of inertia in the longitudinal section, to which the weight of the lens unit 3 is directly related, is much larger than the moment of inertia in the transverse section. In order to eliminate the moment of inertia of the above, no additional laminated piezoelectric element is used, and by simply mounting two laminated piezoelectric elements in the vertical direction, the unnecessary rotational moment can be sufficiently minimized. Therefore, driving with three or more stacked layer type piezoelectric elements simply increases the weight of the optical head and does not improve the frequency characteristics.

As described above, according to the arrangement of the laminated piezoelectric element of the present invention, the frequency characteristic of the optical head responds stably with a constant displacement up to 10 KHz at a constant input voltage, and the phase characteristic is flat. Shows the peculiar characteristic peculiar to the piezoelectric element. Therefore, it is possible to meet the demand with sufficient margin.

[0022]

[Effect of the device]

 As described in detail above, according to the optical head of the optical disk device of the present invention, the optical head can be provided separately from the movable body, and the number of laminated piezoelectric elements is suppressed to the required minimum. Therefore, the weight of the optical head can be reduced.

Further, the two laminated piezoelectric elements are arranged so as not to obstruct the path of the focused light and not to generate an unnecessary rotational moment in the lens unit. Furthermore, the laminated piezoelectric element is used. By providing an access function to the optical head itself, a composite type access mechanism that drives the linear motor section in the frequency band below several hundreds of Hz and the laminated piezoelectric element in the band above that range. Since it can be realized and the weight of the optical head is reduced as described above, it is possible to realize an optical head capable of responding to an extremely high frequency.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of an optical head of the present invention.

FIG. 2 is a vertical cross-sectional view through the center of the objective lens of the optical head unit of the present invention.

FIG. 3 is a schematic perspective view when one laminated piezoelectric element is mounted.

FIG. 4 is a top view of a main part of the optical head unit in FIG.

FIG. 5 is a vertical cross-sectional view of an optical head portion when one laminated piezoelectric element is mounted.

FIG. 6 is a schematic perspective view of a conventional optical head and a movable device.

FIG. 7 is a longitudinal sectional view passing through the center of an objective lens of a conventional optical head unit.

[Explanation of symbols]

1 ... Magnetic yoke, 2 ... Movable body, 3 ... Lens unit, 9
... Focused light, 10 ... Prism lens, 11 ... Objective lens,
12 ... Multilayer piezoelectric element, 16 ... Centroid line, 17 ... Optical disc surface, A ... Optical disc, P ... Centroid.

Claims (1)

[Scope of utility model registration request] 1. An optical head of an optical disc apparatus, comprising: a lens unit having an objective lens and a prism lens in a cylindrical body; and a movable body for moving the lens unit in a radial direction of the optical disc. The unit is fixed to the movable body via two laminated piezoelectric elements, and is equidistant in the vertical direction with respect to a horizontal center of gravity line passing through the center of gravity of the lens unit, and An optical disk device, wherein the two laminated piezoelectric elements are arranged at a position where focused light of a laser beam for reading a signal from the optical disk passes between the two laminated piezoelectric elements. Optical head.